The Magma feeding system of Somma-Vesuvius (Italy)strato-volcano:new inferences from a review of geochemical and Sr,Nd,Pb and O isotope data. Volcanism in the Campania Plain: Vesuvius, Campi Flegrei and Ignimbrites

A large database of major, trace and isotope (Sr, Nd, Pb, O) data exists for rocks produced by the volcanic activity
of Somma-Vesuvius volcano. Variation diagrams strongly suggest a major role for evolutionary processes such
as fractional crystallization, contamination, crystal trapping and magma mixing, occurring after magma genesis
in the mantle. Most mafic magmas are enriched in LILE (K, Rb, Ba), REE (Ce, Sm) and Y, show small Nb–Ta
negative anomalies, and have values of Nb/Zr at about 0.15. Enrichments in LILE, REE, Nb and Ta do not
correlate with Sr isotope values or degree of both K enrichment and silica undersaturation. The results indicate
mantle source heterogeneity produced by slab-derived components beneath the volcano. However, the Sr isotope
values of Somma-Vesuvius increase from 0.7071 up to 0.7081 with transport through the uppermost 11–12 km
of the crust. The Sr isotope variation suggests that the crustal component affected the magmas during ascent
through the lithosphere to the surface. Our new geochemical assessment based on chemical, isotopic and fluid
inclusion data points to the existence of three main levels of magma storage. Two of the levels are deep and may
represent long-lived reservoirs, and an uppermost crustal level that probably coincides with the volcanic conduit.
The deeper level of magma storage is deeper than 12 km and fed the 1944 AD eruption. The intermediate level
coincides with the seismic discontinuity detected by Zollo et al. (1996) at about 8 km. This intermediate level
supplies magmas with 87Sr/86Sr values between 0.7071 and 0.7074, and δO18 8‰ that typically erupted both
during interplinian (i.e. 1906 AD) and sub-plinian (472 AD, 1631 AD) events. The shallowest level of magma storage
at about 5 km was the site of magma chambers for the Pompei and Avellino eruptions. New investigations
are necessary to verify the proposed magma feeding system.